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feat(javascript): write x ? y : x as x && y in the minifier - #22502
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Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 2 remain after this review. 📝 WalkthroughWalkthroughThe improvement phase adds rewrites for selected conditional expressions. Unit tests cover rewritten and preserved cases. Minifier comparison data records updated source lists and gzip-size results. ChangesConditional expression optimization
Suggested labels: Priority: ⬇️ Low Change: Feature Merge Risk: ⚪ Minimal · up to The change adds conditional-expression size optimizations with safeguards for globals, getter rereads, and optional chains. No concrete merge-blocking risk was identified from the supplied evidence. 🚥 Pre-merge checks | ✅ 3 | ❓ 1❌ Failed checks (1 inconclusive)
✅ Passed checks (3 passed)
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Inline comments:
Review comments at @lib/javascript/syntax-printer.js:
- Line 16945: Update the conditional-to-logical rewrite guard near the
`test.definition === alternate.definition` check to require `readsAlike(test,
compressor)` before replacing the alternate. Preserve the existing definition
check and avoid applying this rewrite when repeated reads may differ.
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📒 Files selected for processing (5)
lib/javascript/syntax-printer.jstest/helpers/oxcSmaller.jstest/helpers/swcSmaller.jstest/specCases/minify-corpora.spectest.jstest/unitCases/syntax-printer.unittest.js
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- test/helpers/swcSmaller.js
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npm i -D webpack@https://pkg.pr.new/webpack@a42343f
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Types CoverageCoverage after merging feat/minify-mirrored-conditionals into main will be
Coverage Report |
Generated code sizeComparing base (
Read No asset changed size. No runtime gained or lost a runtime module. Built |
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #22502 +/- ##
==========================================
+ Coverage 95.66% 96.09% +0.43%
==========================================
Files 773 773
Lines 124881 124906 +25
Branches 40914 40926 +12
==========================================
+ Hits 119463 120025 +562
+ Misses 5418 4881 -537
Flags with carried forward coverage won't be shown. Click here to find out more. ☔ View full report in Codecov by Harness. 🚀 New features to boost your workflow:
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Merging this PR will degrade performance by 82.92%
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| Mode | Benchmark | BASE |
HEAD |
Efficiency | |
|---|---|---|---|---|---|
| ❌ | Memory | benchmark "side-effects-reexport", scenario '{"name":"mode-development-rebuild","mode":"development","watch":true}' |
154.3 KB | 903.2 KB | -82.92% |
Tip
Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.
Comparing feat/minify-mirrored-conditionals (6cc0885) with main (86d31e0)
Footnotes
-
6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩
What terser does for `x ? x : y` and `a ? b : (c, b)`, mirrored: `x ? y : x` is written `x && y` and `a ? (c, b) : b` as `(a && c), b`. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
`fixture/issues/11684/class-decl` is no bigger than swc's output since the latest minifier changes on `main`. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
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Inline comments:
Review comments at @lib/javascript/syntax-printer.js:
- Around line 17800-17841: Update the equivalence checks used by
`A.isEquivalent` for `PropAccess`, `Dot`, and `DotHash` to compare each node’s
`optional` flag before treating property accesses as equivalent. Preserve the
existing property-name and quote checks so conditional-expression rewrites do
not merge accesses with different optional-chain behavior.
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📒 Files selected for processing (5)
lib/javascript/syntax-printer.jstest/helpers/oxcSmaller.jstest/helpers/swcSmaller.jstest/specCases/minify-corpora.spectest.jstest/unitCases/syntax-printer.unittest.js
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- test/helpers/swcSmaller.js
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…tional links `isEquivalent` reads `a?.b.c` and `a.b?.c` as one, as terser's `equivalent_to` does, so `f ? (g(), a?.b.c) : a.b?.c` became a read of `a.b?.c` that throws where `a` is nullish. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
#22473 counts a conversion as code that may run, so the value #22499's improved case moved past `console` now has effects and stays put; it now moves a comparison, which converts nothing. And #22499 now shortens #22473's literal case, whose assertion holds the output to terser's, so that case runs with the improve phase off. With both in, `vercel/ms` is bigger than oxc's output again (787 against 781 gzip), so it goes back on OXC_SMALLER, where #22499 had retired it on its own. And #22502 leaves terser's `side_effects_cascade_3` no bigger than oxc's, so it comes off. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
#22473 counts a conversion as code that may run, so the value #22499's improved case moved past `console` now has effects and stays put; it now moves a comparison, which converts nothing. And #22499 now shortens #22473's literal case, whose assertion holds the output to terser's, so that case runs with the improve phase off. With both in, `vercel/ms` is bigger than oxc's output again (787 against 781 gzip), so it goes back on OXC_SMALLER, where #22499 had retired it on its own. And #22502 leaves terser's `side_effects_cascade_3` no bigger than oxc's, so it comes off. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
#22473 counts a conversion as code that may run, so the value #22499's improved case moved past `console` now has effects and stays put; it now moves a comparison, which converts nothing. And #22499 now shortens #22473's literal case, whose assertion holds the output to terser's, so that case runs with the improve phase off. With both in, `vercel/ms` is bigger than oxc's output again (787 against 781 gzip), so it goes back on OXC_SMALLER, where #22499 had retired it on its own. And #22502 leaves terser's `side_effects_cascade_3` no bigger than oxc's, so it comes off. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
#22521) #22473 counts a conversion as code that may run, so the value #22499's improved case moved past `console` now has effects and stays put; it now moves a comparison, which converts nothing. And #22499 now shortens #22473's literal case, whose assertion holds the output to terser's, so that case runs with the improve phase off. With both in, `vercel/ms` is bigger than oxc's output again (787 against 781 gzip), so it goes back on OXC_SMALLER, where #22499 had retired it on its own. And #22502 leaves terser's `side_effects_cascade_3` no bigger than oxc's, so it comes off. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
…22504) * perf(javascript): print a mangled program once, naming it afterwards The mangle phase printed the tree twice: once to count the characters the names are chosen from, once for the result. It now prints before the names are chosen, recording where each name and each import or export `as` clause lies, counts the characters off that text and writes the names into it once chosen, moving the source map's columns with them. The `let` declarations the improve phase left for after naming are written before that print, and the count puts back what they changed. A print that wrote a comment, shebang or preamble still counts with a print of its own, as those are not counted. * test(javascript): fit two minifier tests to #22473 and #22499 together #22473 counts a conversion as code that may run, so the value #22499's improved case moved past `console` now has effects and stays put; it now moves a comparison, which converts nothing. And #22499 now shortens #22473's literal case, whose assertion holds the output to terser's, so that case runs with the improve phase off. With both in, `vercel/ms` is bigger than oxc's output again (787 against 781 gzip), so it goes back on OXC_SMALLER, where #22499 had retired it on its own. And #22502 leaves terser's `side_effects_cascade_3` no bigger than oxc's, so it comes off. Claude-Session: https://claude.ai/code/session_01ViD41i2KdwwGxrDk7yrjeD
Summary
A step from oxc's
peephole/esbuild.rsandminimize_conditional_expression.rsgroups. terser already rewrites two conditionals, but not their mirror images:x ? x : y→x || yx ? y : xa ? b : (c, b)→(a || c), ba ? (c, b) : bThe
improvephase now writes the mirrored forms the same way:x ? y : x→x && y, where bothxare the same declared binding. A global or a name awithcan rebind is skipped, since a getter may answer each read differently;a ? (c, b) : b→(a && c), b.Minified against
main:benches/full,passes: 2lib/(781 files,ecma: 2020)The corpora print what they should:
oxcSmaller.jsand 3 fromswcSmaller.js;IMPROVED_YET_BIGGER.What kind of change does this PR introduce?
feat
Did you add tests for your changes?
Yes, in
test/unitCases/syntax-printer.unittest.js:Does this PR introduce a breaking change?
No.
If relevant, what needs to be documented once your changes are merged or what have you already documented?
docs/syntax.mdwill list this rewrite with the other minifier changes in one docs update.Use of AI
Written with Claude Code: it found the asymmetry in terser's conditional rules, wrote the change and tests, and ran the corpora and size checks; I reviewed the result.
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